Pulsed field studies of magnetotransport in semiconductor heterostructures

High field magnetotransport in two classes of semiconductor heterostructures has been studied: parallel transport in InAs/(Ga,In)Sb double heterojunctions and superlattices at low temperatures (300 mK-4.2 K), and vertical transport in GaAs/AlAs short-period superlattices at 150-300 K. The experiments mainly used the Oxford pulsed magnet (∼45 T, ∼15 ms pulses). The development of the data acquisition system and experimental techniques for magnetotransport are described, including corrections to the data, required because of the rapidly changing magnetic field. Previous studies of magnetotransport in InAs/GaSb double heterojunctions are reviewed: this electron-hole system shows compensated quantum Hall plateaux, with ρxy dips accompanied by 'anomalous' peaks in σxx. New data show a peak between ν=1 plateaux; this behaviour and the temperature dependence of the 'anomalous' σxx peaks are explained by considering the movement of the Fermi level amongst anticrossing electron- and hole-like levels. InAs/(Ga,In)Sb superlattices with electron:hole density ratios close to 1 exhibit large oscillations in the resistivity (maxima typically ∼20-30 x higher than minima) and conductivity components. Deep minima in ρxy alternate with low-integer plateaux. The magnetotransport in various ideal structures is considered, to explain the experimental results. The growth of a novel structure has allowed clearer observation of the behaviour of ρxx (giant maxima) and ρxy (zeroes or maxima) when the contributions from each well to σxx and σxy approach zero. Measurements of the high field magnetotransport peak positions show that the band overlap is increased by growing 'InSb' rather than 'GaAs' interfaces (∼20% increase), increasing the indium in the (Ga,In)Sb (∼30% increase per 10% In), or growing along [111] instead of [001] (∼30% increase). Magnetophonon resonance in short-period GaAs/AlAs superlattices causes strong, electric field-dependent vertical conductance minima, observed for both GaAs and AlAs LO phonons; a resonance maximum is observed at 250 K. A qualitative Bloch transport explanation is given for this striking behaviour, and theoretical interest is anticipated. (author)